1. Field of the Invention
The present invention relates to electric power steering for reducing a required steering force in a steering system by means of mechanical power of a motor. More particularly, the present invention relates to an electric power steering control system for preventing overheating of the motor and a motor drive circuit.
2. Description of the Related Art
As an example of an art having an objective of preventing overheating of a motor and a motor drive circuit, there exists an electric power steering device described in Japanese Patent Application Laid-open No. 11-59444.
According to the above-mentioned conventional art, a heat sensor is provided on a periphery of the motor or the motor drive circuit portion, a motor current limit value is calculated based on a heating value estimated from a temperature detected by the temperature sensor and a current of the motor, and the motor current is limited by means of this calculated motor current limit value. Accordingly, the overheating of the motor is prevented.
According to the above-mentioned conventional art, the heat sensor is provided to a vicinity of a location generating heat, and control for preventing overheating is realized by means of directly detecting an ambient temperature of the location generating heat. However, in an actual system there are cases when it is difficult, for reasons of construction and cost, to place the temperature sensor in the vicinity of the heat-generating part. In such cases, prevention of overheating becomes problematic in the conventional art. Furthermore, in a case when there exists a plurality of heat-generating parts (or parts at which it is desirable to estimate the temperature thereof), a plurality of temperature sensors and I/F circuits need to be installed. Therefore, there was a problem that it was disadvantageous in terms of cost and miniaturization.